OBJECTIVE Giant (>or=25 mm) intracranial aneurysms (IA) have an extremely poor natural history and continue to confound modern techniques for management. Currently, there is a dearth of large series examining endovascular treatment of giant IAs only. METHODS We reviewed long-term clinical and radiological outcome from a series of 39 consecutive giant IAs treated with endovascular repair in 38 patients at 2 tertiary referral centers. Data were evaluated in 3 ways: on a per-treatment session basis for each aneurysm, at 30 days after each patient's final treatment, and at the last known follow-up examination. RESULTS Ten (26%) aneurysms were ruptured. At the last angiographic follow-up examination (21.5 +/- 22.9 months), 95% or higher and 100% occlusion rates were documented in 64 and 36% of aneurysms, respectively, with parent vessel preservation maintained in 74%. Stents were required in 25 aneurysms. Twenty percent of treatment sessions resulted in permanent morbidity, and death within 30 days occurred after 8% of treatment sessions. On average, 1.9 +/- 1.1 sessions were required to treat each aneurysm, with a resulting cumulative per-patient mortality of 16% and morbidity of 32%. At the last known clinical follow-up examination (mean, 24.8 +/- 24.8 months), 24 (63%) patients had Glasgow Outcome Scale scores of 4 or 5 ("good" or "excellent"), 10 patients had worsened neurological function from baseline (26% morbidity), and 11 had died (29% mortality). CONCLUSIONS We present what is to our knowledge the largest series to date evaluating outcome after consecutive giant IAs treated with endovascular repair. Giant IAs carry a high risk for surgical or endovascular intervention. We hope critical and honest evaluation of treatment results will ensure continued improvement in patient care.